1995 Cummins 8.3 Mechanical 300 HP-- Very Low Power

[dougja1960]

I have a 1995 Monaco Executive with a Cummins 8.3 mechanical 300 hp.

I just bought it and it had been sitting for about 3 years. I starts just find and idles fine but when I put it in gear and star to go, I have no power. I can never get the coach to go more than about 35 mph on flat ground. If I try to push on the accelerator to go faster it just gears down and this is in any gear. I would sure appreciate any help I can get.

[Walt2137]

I would change the fuel filters first, be sure to change the primary first then start the coach before changing the secondary filter. I use a nipple to close up the fuel outlet on the filter and prefill using the outside holes, Some will say not to pre fill but I have always prefilled by blocking the outlet side. Also check to see if the pac brake is part way closed. That year Monaco coach had the King Control fuel and cruse that gave trouble, you would probaly need a mechanic that is familiar with the King Control or do a google.

[wolfe10]

Agree with Walt.

Replace both fuel filters.

Smell the diesel. Does it smell like diesel, or has it "turned". If turned, it will need to be replaced.

While you watch the throttle at the engine, with the engine off, have someone step on the throttle. Verify that the throttle is opening all the way.

[dave111451]

Any smoke from exhaust on acceleration? What color if there is? Plugged air filter or mouse nest some where, turbo hose rotted off or off. Turbo bad?

[ticat900]

I would change the fuel filters first, be sure to change the primary first then start the coach before changing the secondary filter. I use a nipple to close up the fuel outlet on the filter and prefill using the outside holes, Some will say not to pre fill but I have always prefilled by blocking the outlet side. Also check to see if the pac brake is part way closed. That year Monaco coach had the King Control fuel and cruse that gave trouble, you would probaly need a mechanic that is familiar with the King Control or do a google.

Fuel filters and definitely prefill but not to worry about pluging fuel outlet just make sure the fuel and container and fuel your using is super clean. Exhaust brake frozen closed will definitely cause this problem. Plugged air filter, turbo not working for sure will cause the problem or broken/badly leaking intercooler hose.

[actionjackson]

Crawl under the coach. Locate the turbo and wastegate valve. There should be a fuel air tube that runs out of the wastgate. Check and make sure this tube is not broken or severed. This air tube is vital to supplying air to the fuel pump. No air no (reduced) power.

[ticat900]

The fuel air tube that runs out of the turbo waste gate that supplies air to the fuel pump?? Never heard that one before?

There is a small vacuum tube that regulates the tubro boost pressure.

[cmarq]

The tube that regulates the fuel pump comes out of the intake manifold to the fuel pump. The device in the pump is called an AFC (air fuel control) the afc is a diaphragm against spring pressure it prevents the fuel pump from supplying too much fuel until turbo boost is supplying the right amount of air to prevent black smoke. The Bubba's refer to it as a smoke / power control. If it is set right and working properly it will not decrease power. If the diaphgram is ruptured or the line is leaking or you have an air loss in the charge air cooler or piping it will not go to full fuel and result in a power loss. you may save time and money having it checked at a GOOD diesel shop.

cmarq. 40 years as cummins tech.

[ticat900]

Thanks cmarq as that explanation makes a lot more sense.

[hermanmullins]

If the coach has been setting for three years, I would change every filter on the coach, the oil, all belts, put in fuel additives, have the coolant checked and check out the transmission. It will be costly but well worth it all.

Herman

PS, check the dates on the tires also.

[dickandlois]

Dougja1,

Welcome to the FMCA Forum!

Been following this thread.

The members posted some real good information on what to check, replace and why.

The only item I would add is to have the valve train adjusted,(lifter clearance checked) once you get the power level up to where it should be.

Rich.

[dougja1960]

I am the original poster of this question. Some how my account Dougja1 got inactivated.

At any rate I finally took the coach into a diesel mechanic and the first thing he did was to check the rubber boot that mates the turbo charger to the air charger and sure enough there was a split in it about 2 inched long on the back side where I couldn't see. He installed a new one and the coach now runs like a champ.

Thanks for all of the suggestions.

[hermanmullins]

Doug,

Thanks for the update. Nice to know how it turned out.

Herman

[wildebill308]

Glad you found the problem and it wasn't something major.

Bill